Dental calculus, or tartar, is a recurring calcified deposit on the surfaces of the teeth of many mammals, including humans, and domesticated dogs and cats. It is generally recognized that dental calculus develops in a sequential process that involves the accumulation of dental plaque and the subsequent calcification of the plaque by saliva, which contains very high concentrations of calcium and phosphate. Although calculus, per se, is not directly responsible for the development of oral diseases, it is considered to be a secondary, or contributing factor in the development of periodontal disease because: (1) its presence on the teeth serves as a local irritant to the adjacent soft tissues, eliciting an inflammatory response (and soft tissue inflammation is the initial phase of periodontal disease); (2) it interferes with the normal cleansing of the tooth surfaces, which occurs during the mastication of food or through the performance of conventional oral hygiene procedures, such as tooth brushing and flossing; and (3) by virtue of its porosity, it harbors bacterial toxins, which exacerbate periodontal disease formation.
Consequences of periodontal disease can include systemic infection, alveolar bone recision, tooth decay and loss, and adverse mouth and breath odors. Once formed, calculus deposits can only be removed through dental prophylaxis or other mechanical procedures. Thus, the prevention of dental calculus is of importance not only for cosmetic reasons, but also because of dental calculus' secondary role in the development of periodontal disease, and the resultant systemic infections, alveolar bone recision, tooth loss and adverse mouth and breath odors.
Currently, dental calculus formation may be prevented in three ways. First, dental calculus formation can be prevented by meticulous, daily removal of dental plaque prior to its calcification. Second, dental calculus formation can be prevented by the daily application of crystal growth inhibitors that interfere with the calcification of dental plaque by saliva. Recognized crystal growth inhibitors include various soluble pyrophosphates, sodium tripolyphosphate, soluble diphosphonates, and certain soluble zinc compounds, such as zinc chloride. These crystal growth inhibitors arc used in dentifrices and mouthwashes for prevention of calculus formation in humans and animals. Soluble pyrophosphates are currently cooked or baked into the dough of commercially-prepared foods for domesticated dogs and cats in order to prevent or reduce dental calculus formation in these animals. Third, dental calculus formation may be prevented by the use of sodium hexametaphosphate. U.S. Pat. No. 5,296,217, issued on Mar. 22, 1994, and U.S. Pat. No. 5,618,518, issued on Apr. 8, 1997, disclose that sodium hexametaphosphate can prevent or reduce calculus build-up when applied as a coating to dry pet foods, pet chew products, or when mixed with moist foods. Sodium hexametaphosphate is currently incorporated into some commercially-available dry dog and cat diets, as well as snack foods, to prevent dental calculus formation.
However, many food products arc incompatible with sodium hexametaphosphate. For example, some commercially-prepared dry foods for cats and dogs are surface coated with phosphoric acid, which is used as an organoleptic and a palatant. In addition, some commercially-prepared moist foods for cats and dogs contain phosphoric acid, for the same reasons mentioned above. When sodium hexametaphosphate is applied as a final coating over a food product which has been coated with or contains phosphoric acid, the hexametaphosphate is converted to other forms of phosphate, predominantly orthophosphate. This chemical conversion destroys the ability of the hexametaphosphate to prevent calculus formation. Thus, incorporation of sodium hexametaphosphate into animal foods previously coated with or containing phosphoric acid actually negates the beneficial effects of sodium hexametaphosphate.
Therefore, a need exists for food products or methods that are useful to control or reduce calculus formation in animals, and that are suitable for, and compatible with, foods treated with or containing phosphoric acid.